1. Field of the Invention
The present invention relates to a distributed oscillator, and more particularly, to a high frequency distributed oscillator using coupled transmission lines.
2. Background of the Related Art
In an oscillation circuit, an oscillator using an inductor and a capacitor as a resonator has been widely used.
In a several GHz bandwidth, however, if a circuit in which an application frequency operates 10 GHz or more is used although not becoming a significant problem in analyzing the circuit, parasitic component or parasitic parameters are generated in the inductor and the capacitor.
That is, capacitance of the capacitor exists in the conductor of the inductor, and inductance component also exists in the plate of the capacitor.
An oscillator is difficult to design so that it operates at a desired frequency and a frequency tuning characteristic is also significantly lowered, because of the parasitic component or parasitic parameters.
There is a disadvantage in that it is difficult to design and implement a passive element due to the parasitic parameters.
Recently, in order to overcome this disadvantage, technology for a distributed oscillator has been proposed.
FIG. 1 is a circuit diagram illustrating the operational principle of a conventional distributed oscillator.
Referring to FIG. 1, the conventional distributed oscillator includes active elements M11 to M15 respectively having first to third terminals, which are responsible for signal amplification, and transmission lines 111 to 120.
A DC voltage is applied to the transmission line 119, and an output signal is transmitted through the transmission line 120.
The first terminals of the active elements M11 to M15 are connected between the transmission lines 111, 112, 113 and 114, so that signals are amplified due to the active elements M11 to M15.
In this time, signals inputted to the second terminals of the active elements M11 to M15 are transmitted through the transmission lines 115, 116, 117 and 118.
Furthermore, if amplified signals generated from the active elements M11 to M15 have the same phase, it can be represented as the sum of those amplified signals.
That is, if a signal 131 amplified in the active element M11 has the same phase as that amplified in the active element M12, they are added to become a summed and amplified signal 132.
As such, if the above process is repeatedly performed between the active elements M11 to M15, an amplified signal 134 becoming the sum of the signals amplified in the active elements M11 to M15 is obtained. Consequently, the summed signal 134 is feedbacked to the second terminals of the active elements M11 to M15, thus forming a distributed oscillator.
Through the above-described construction and operation, the distribution type oscillator is advantageous in that it can operate up to the maximum frequency of oscillation (fmax) of an active element in such a manner that the distributed amplifier is oscillated by feedbacking its output terminal to its input terminal.
However, the distributed oscillator is disadvantageous in that the chip size increases because a ground line has to be formed at both sides of a signal line when designing the distributed oscillator.